Originally published May 1997
Never fly around with yellow oil pressure!
On a reciprocating engine, there should be an oil pressure indicator with a green sector for normal oil pressure, and yellow above and below. If oil pressure has been normal and green for some time and then rises into the high yellow, one or more of all those narrow oil holes and galleries has been clogged. No oil to some bearings. The regulating valve cannot handle the large change in flow, hence yellow pressure. Pulling off to idle and landing with control is much better and cheaper than waiting for seizure.
At the pressure of green/low yellow a valve opens to blow oil into the inside of pistons, the only heat dissipation they get. So at low yellow oil pressure, no piston cooling. (This is acceptable at idle.) Again, pulling off to idle and landing with control is much better and cheaper than waiting until it seizes.
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 20 December 1997